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Use "dollar-single-quotes" to escape shell-sensitive strings

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Also called "ANSI-C Quoting" in info:(bash) ANSI-C Quoting.

The escaping rules are a POSIX proposal, and are described in
http://austingroupbugs.net/view.php?id=249. There's a lot of back-and-forth on
the details of escaping of control characters, but we'll be only using a small
subset of the syntax that is common to all proposals and is widely supported.
Unfortunately dash and fish and maybe some other shells do not support it (see
the man page patch for a list).

This allows environment variables to be safely exported using show-environment
and imported into the shell. Shells which do not support this syntax will have
to do something like
    export $(systemctl show-environment|grep -v '=\$')
or whatever is appropriate in their case. I think csh and fish do not support
the A=B syntax anyway, so the change is moot for them.

Fixes #5536.

v2:
- also escape newlines (which currently disallowed in shell values, so this
  doesn't really matter), and tabs (as $'\t'), and ! (as $'!'). This way quoted
  output can be included directly in both interactive and noninteractive bash.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek 2017-06-11 15:24:07 -04:00
parent 42d3bf86bb
commit 804ee07c13
8 changed files with 134 additions and 33 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

25
man/systemctl.xml
View File

@ -1495,11 +1495,26 @@ Jan 12 10:46:45 example.com bluetoothd[8900]: gatt-time-server: Input/output err
<term><command>show-environment</command></term>
<listitem>
<para>Dump the systemd manager environment block. The
environment block will be dumped in straight-forward form
suitable for sourcing into a shell script. This environment
block will be passed to all processes the manager
spawns.</para>
<para>Dump the systemd manager environment block. This is the environment
block that is passed to all processes the manager spawns. The environment
block will be dumped in straight-forward form suitable for sourcing into
most shells. If no special characters or whitespace is present in the variable
values, no escaping is performed, and the assignments have the form
<literal>VARIABLE=value</literal>. If whitespace or characters which have
special meaning to the shell are present, dollar-single-quote escaping is
used, and assignments have the form <literal>VARIABLE=$'value'</literal>.
This syntax is known to be supported by
<citerefentry project='die-net'><refentrytitle>bash</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry project='die-net'><refentrytitle>zsh</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry project='die-net'><refentrytitle>ksh</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
and
<citerefentry project='die-net'><refentrytitle>busybox</refentrytitle><manvolnum>1</manvolnum></citerefentry>'s
<citerefentry project='die-net'><refentrytitle>ash</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
but not
<citerefentry project='die-net'><refentrytitle>dash</refentrytitle><manvolnum>1</manvolnum></citerefentry>
or
<citerefentry project='die-net'><refentrytitle>fish</refentrytitle><manvolnum>1</manvolnum></citerefentry>.
</para>
</listitem>
</varlistentry>
<varlistentry>

38
src/basic/escape.c
View File

@ -441,10 +441,16 @@ char *octescape(const char *s, size_t len) {
}
static char *strcpy_backslash_escaped(char *t, const char *s, const char *bad) {
static char *strcpy_backslash_escaped(char *t, const char *s, const char *bad, bool escape_tab_nl) {
assert(bad);
for (; *s; s++) {
if (escape_tab_nl && IN_SET(*s, '\n', '\t')) {
*(t++) = '\\';
*(t++) = *s == '\n' ? 'n' : 't';
continue;
}
if (*s == '\\' || strchr(bad, *s))
*(t++) = '\\';
@ -461,20 +467,21 @@ char *shell_escape(const char *s, const char *bad) {
if (!r)
return NULL;
t = strcpy_backslash_escaped(r, s, bad);
t = strcpy_backslash_escaped(r, s, bad, false);
*t = 0;
return r;
}
char *shell_maybe_quote(const char *s) {
char* shell_maybe_quote(const char *s, EscapeStyle style) {
const char *p;
char *r, *t;
assert(s);
/* Encloses a string in double quotes if necessary to make it
* OK as shell string. */
/* Encloses a string in quotes if necessary to make it OK as a shell
* string. Note that we treat benign UTF-8 characters as needing
* escaping too, but that should be OK. */
for (p = s; *p; p++)
if (*p <= ' ' ||
@ -485,17 +492,30 @@ char *shell_maybe_quote(const char *s) {
if (!*p)
return strdup(s);
r = new(char, 1+strlen(s)*2+1+1);
r = new(char, (style == ESCAPE_POSIX) + 1 + strlen(s)*2 + 1 + 1);
if (!r)
return NULL;
t = r;
*(t++) = '"';
if (style == ESCAPE_BACKSLASH)
*(t++) = '"';
else if (style == ESCAPE_POSIX) {
*(t++) = '$';
*(t++) = '\'';
} else
assert_not_reached("Bad EscapeStyle");
t = mempcpy(t, s, p - s);
t = strcpy_backslash_escaped(t, p, SHELL_NEED_ESCAPE);
if (style == ESCAPE_BACKSLASH)
t = strcpy_backslash_escaped(t, p, SHELL_NEED_ESCAPE, false);
else
t = strcpy_backslash_escaped(t, p, SHELL_NEED_ESCAPE_POSIX, true);
*(t++)= '"';
if (style == ESCAPE_BACKSLASH)
*(t++) = '"';
else
*(t++) = '\'';
*t = 0;
return r;

23
src/basic/escape.h
View File

@ -31,13 +31,30 @@
/* What characters are special in the shell? */
/* must be escaped outside and inside double-quotes */
#define SHELL_NEED_ESCAPE "\"\\`$"
/* can be escaped or double-quoted */
#define SHELL_NEED_QUOTES SHELL_NEED_ESCAPE GLOB_CHARS "'()<>|&;"
/* Those that can be escaped or double-quoted.
*
* Stricly speaking, ! does not need to be escaped, except in interactive
* mode, but let's be extra nice to the user and quote ! in case this
* output is ever used in interactive mode. */
#define SHELL_NEED_QUOTES SHELL_NEED_ESCAPE GLOB_CHARS "'()<>|&;!"
/* Note that we assume control characters would need to be escaped too in
* addition to the "special" characters listed here, if they appear in the
* string. Current users disallow control characters. Also '"' shall not
* be escaped.
*/
#define SHELL_NEED_ESCAPE_POSIX "\\\'"
typedef enum UnescapeFlags {
UNESCAPE_RELAX = 1,
} UnescapeFlags;
typedef enum EscapeStyle {
ESCAPE_BACKSLASH = 1,
ESCAPE_POSIX = 2,
} EscapeStyle;
char *cescape(const char *s);
char *cescape_length(const char *s, size_t n);
size_t cescape_char(char c, char *buf);
@ -51,4 +68,4 @@ char *xescape(const char *s, const char *bad);
char *octescape(const char *s, size_t len);
char *shell_escape(const char *s, const char *bad);
char *shell_maybe_quote(const char *s);
char* shell_maybe_quote(const char *s, EscapeStyle style);

2
src/core/job.c
View File

@ -741,7 +741,7 @@ static void job_print_status_message(Unit *u, JobType t, JobResult result) {
if (t == JOB_START && result == JOB_FAILED) {
_cleanup_free_ char *quoted;
quoted = shell_maybe_quote(u->id);
quoted = shell_maybe_quote(u->id, ESCAPE_BACKSLASH);
manager_status_printf(u->manager, STATUS_TYPE_NORMAL, NULL, "See 'systemctl status %s' for details.", strna(quoted));
}
}

2
src/environment-d-generator/environment-d-generator.c
View File

@ -78,7 +78,7 @@ static int load_and_print(void) {
t = strchr(*i, '=');
assert(t);
q = shell_maybe_quote(t + 1);
q = shell_maybe_quote(t + 1, ESCAPE_BACKSLASH);
if (!q)
return log_oom();

2
src/shared/bus-unit-util.c
View File

@ -860,7 +860,7 @@ static void log_job_error_with_service_result(const char* service, const char *r
assert(service);
service_shell_quoted = shell_maybe_quote(service);
service_shell_quoted = shell_maybe_quote(service, ESCAPE_BACKSLASH);
if (extra_args) {
_cleanup_free_ char *t;

26
src/systemctl/systemctl.c
View File

@ -47,6 +47,7 @@
#include "dropin.h"
#include "efivars.h"
#include "env-util.h"
#include "escape.h"
#include "exit-status.h"
#include "fd-util.h"
#include "fileio.h"
@ -5573,6 +5574,24 @@ static int reset_failed(int argc, char *argv[], void *userdata) {
return r;
}
static int print_variable(const char *s) {
const char *sep;
_cleanup_free_ char *esc = NULL;
sep = strchr(s, '=');
if (!sep) {
log_error("Invalid environment block");
return -EUCLEAN;
}
esc = shell_maybe_quote(sep + 1, ESCAPE_POSIX);
if (!esc)
return log_oom();
printf("%.*s=%s\n", (int)(sep-s), s, esc);
return 0;
}
static int show_environment(int argc, char *argv[], void *userdata) {
_cleanup_(sd_bus_error_free) sd_bus_error error = SD_BUS_ERROR_NULL;
_cleanup_(sd_bus_message_unrefp) sd_bus_message *reply = NULL;
@ -5602,8 +5621,11 @@ static int show_environment(int argc, char *argv[], void *userdata) {
if (r < 0)
return bus_log_parse_error(r);
while ((r = sd_bus_message_read_basic(reply, SD_BUS_TYPE_STRING, &text)) > 0)
puts(text);
while ((r = sd_bus_message_read_basic(reply, SD_BUS_TYPE_STRING, &text)) > 0) {
r = print_variable(text);
if (r < 0)
return r;
}
if (r < 0)
return bus_log_parse_error(r);

49
src/test/test-escape.c
View File

@ -86,25 +86,52 @@ static void test_shell_escape(void) {
test_shell_escape_one("foo:bar,baz", ",:", "foo\\:bar\\,baz");
}
static void test_shell_maybe_quote_one(const char *s, const char *expected) {
_cleanup_free_ char *r;
static void test_shell_maybe_quote_one(const char *s,
EscapeStyle style,
const char *expected) {
_cleanup_free_ char *ret = NULL;
assert_se(r = shell_maybe_quote(s));
assert_se(streq(r, expected));
assert_se(ret = shell_maybe_quote(s, style));
log_debug("[%s] → [%s] (%s)", s, ret, expected);
assert_se(streq(ret, expected));
}
static void test_shell_maybe_quote(void) {
test_shell_maybe_quote_one("", "");
test_shell_maybe_quote_one("\\", "\"\\\\\"");
test_shell_maybe_quote_one("\"", "\"\\\"\"");
test_shell_maybe_quote_one("foobar", "foobar");
test_shell_maybe_quote_one("foo bar", "\"foo bar\"");
test_shell_maybe_quote_one("foo \"bar\" waldo", "\"foo \\\"bar\\\" waldo\"");
test_shell_maybe_quote_one("foo$bar", "\"foo\\$bar\"");
test_shell_maybe_quote_one("", ESCAPE_BACKSLASH, "");
test_shell_maybe_quote_one("", ESCAPE_POSIX, "");
test_shell_maybe_quote_one("\\", ESCAPE_BACKSLASH, "\"\\\\\"");
test_shell_maybe_quote_one("\\", ESCAPE_POSIX, "$'\\\\'");
test_shell_maybe_quote_one("\"", ESCAPE_BACKSLASH, "\"\\\"\"");
test_shell_maybe_quote_one("\"", ESCAPE_POSIX, "$'\"'");
test_shell_maybe_quote_one("foobar", ESCAPE_BACKSLASH, "foobar");
test_shell_maybe_quote_one("foobar", ESCAPE_POSIX, "foobar");
test_shell_maybe_quote_one("foo bar", ESCAPE_BACKSLASH, "\"foo bar\"");
test_shell_maybe_quote_one("foo bar", ESCAPE_POSIX, "$'foo bar'");
test_shell_maybe_quote_one("foo\tbar", ESCAPE_BACKSLASH, "\"foo\tbar\"");
test_shell_maybe_quote_one("foo\tbar", ESCAPE_POSIX, "$'foo\\tbar'");
test_shell_maybe_quote_one("foo\nbar", ESCAPE_BACKSLASH, "\"foo\nbar\"");
test_shell_maybe_quote_one("foo\nbar", ESCAPE_POSIX, "$'foo\\nbar'");
test_shell_maybe_quote_one("foo \"bar\" waldo", ESCAPE_BACKSLASH, "\"foo \\\"bar\\\" waldo\"");
test_shell_maybe_quote_one("foo \"bar\" waldo", ESCAPE_POSIX, "$'foo \"bar\" waldo'");
test_shell_maybe_quote_one("foo$bar", ESCAPE_BACKSLASH, "\"foo\\$bar\"");
test_shell_maybe_quote_one("foo$bar", ESCAPE_POSIX, "$'foo$bar'");
/* Note that current users disallow control characters, so this "test"
* is here merely to establish current behaviour. If control characters
* were allowed, they should be quoted, i.e. \001 should become \\001. */
test_shell_maybe_quote_one("a\nb\001", ESCAPE_BACKSLASH, "\"a\nb\001\"");
test_shell_maybe_quote_one("a\nb\001", ESCAPE_POSIX, "$'a\\nb\001'");
test_shell_maybe_quote_one("foo!bar", ESCAPE_BACKSLASH, "\"foo!bar\"");
test_shell_maybe_quote_one("foo!bar", ESCAPE_POSIX, "$'foo!bar'");
}
int main(int argc, char *argv[]) {
log_set_max_level(LOG_DEBUG);
log_parse_environment();
log_open();
test_cescape();
test_cunescape();
test_shell_escape();